Many mechanical musical instruments, such as player pianos, orchestrions, nickelodeons, band organs, fariground organs, etc., employ a vacuum-operated “tracker bar” for operating musical instruments. Typically, such musical instruments employ perforated paper or paper-like rolls, wherein perforations in the roll effectively encode a musical performance.
The perforations in the paper rolls are arranged into “tracks” or columns, each column corresponding to an appropriately positioned opening in a tracker bar, over which the paper is passed. The openings in the tracker are positioned to align with corresponding “tracks” in the paper roll. The paper roll is fed from a supply spool to a takeup spool, passing over the tracker bar along the way. Typically, each opening in the tracker bar is connected via a signal tube to a control port on a pneumatic valve. In response to perforations in the paper roll, each valve controls a different function. Some valves cause notes to play. Other valves perform functions such as setting expression levels, operating a damper pedal, a soft pedal, or causing the paper roll to rewind.
Original paper music rolls for instruments of the type described above are typically between 60 and 100 years old. Many have deteriorated sufficiently that they can no longer be played. Only a limited selection of newer “recut” rolls is available. Many of the rolls considered best by collectors are the ones that have received the most play, and are therefore in the worst condition.
Recently, considerable effort has been expended in capturing and storing the patterns of perforations on music rolls in digital form on computer-readable media. This has generally been accomplished by means of electrical, pneumatic or optical scanning devices that “read” the perforation patterns on the rolls. As a result, roll performances that might otherwise be lost have been preserved on computer media.
A natural outgrowth of the combined availability of roll performances in digital form and the lack of availability of rolls in good condition has been an interest in adapting pneumatically-operated tracker-bar based instruments to play under computer control, with digital computer equipment providing electrical signals corresponding to perforations in the music rolls to a system of electrically operated pneumatic valves that interface to the signal tubing in a pneumatically operated instrument, effectively mimicking the behavior of a perforated paper roll passing over a tracker bar.
There are several problems with such systems:
1) Most solenoid operated valves were not designed for the high repetition rates and highly variable vacuum levels required by mechanical musical instruments. As a result, they tend to perform poorly in musical applications.
2) Most solenoid operated valves, including organ valves, are relatively large compared to the tiny signal tubes in most pneumatic musical instruments, and space in those musical instruments is often very scarce.
3) A typical player or reproducing piano requires anywhere from 90-100 valves. When individual solenoid valves are employed, the wiring is quite bulky and cumbersome.
4) Depending upon the types of valves used, their mounting, etc, such valve systems can be quite noisy, creating “clicking” noises loud enough to interfere with the music produced by the musical instrument.
Some attempts have been made to interface directly to the tracker bar of the instrument, opening and closing the “ports” of the tracker bar directly by connecting solenoid valves thereto. Unfortunately, the tracker bar port is usually the smallest passage in the pneumatic signal path to the control ports of the valves of the mechanical musical instrument. By creating an even longer path to the valve control ports in the musical instrument and by placing the most restricted part of the pneumatic signal path in the middle of this extended path (i.e., the tracker bar opening itself) considerable flow restriction can be experienced in attempting to operate the instrument, and performance (e.g., response time, repetition rate, etc.) can suffer.